Photodynamic therapy for infected foot ulcers in people with diabetes mellitus: a systematic review

ABSTRACT BACKGROUND: Ulceration of the feet in patients with diabetes is a frequent complication that increases morbidity, mortality, hospitalization, treatment costs, and non-traumatic amputations. OBJECTIVE: To present a systematic review of the treatment of patients with diabetes mellitus and infected foot ulcers using photodynamic therapy. DESIGN AND SETTING: A systematic review was performed in the postgraduate program in nursing at the Universidade da Integração Internacional da Lusofonia Afro-Brasileira, Ceará, Brazil. METHODS: PubMed, CINAHL, Web of Science, EMBASE, Cochrane Library, Scopus, and LILACS databases were screened. The methodological quality, risk of bias, and quality of evidence of each study were assessed. Review Manager was used for the meta-analysis. RESULTS: Four studies were included. They highlighted significantly better outcomes in patient groups treated with photodynamic therapy than those in the control groups that were treated with topical collagenase and chloramphenicol (P = 0.036), absorbent (P < 0.001), or dry covers (P = 0.002). Significant improvements were noted in terms of the microbial load in the ulcers and tissue repair, with a reported reduction in the need for amputation by up to 35 times. Photodynamic therapy resulted in significantly better outcomes between the experimental and control groups (P = 0.04). CONCLUSION: Photodynamic therapy is significantly more effective in treating infected foot ulcers than standard therapies. SYSTEMATIC REVIEW REGISTRATION: International Prospective Register of Systematic Reviews (PROSPERO) - CRD42020214187, https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=214187.


INTRODUCTION
Ulcers in the feet of patients with diabetes mellitus (DM) are a frequent complication and a relevant cause of morbidity and mortality, increased rates of hospitalization and higher treatment costs, and non-traumatic amputations of lower limbs. 1 Approximately 60% of people who undergo amputations do so for infected ulcers in the feet. 2 Infection is one of the leading causes of amputations in patients with DM; due to delayed healing in DM, infections promote exudate, swelling, microbial growth, friability, and hemorrhagic granulation tissue. 3,4 Moreover, when not treated correctly, it increases the risk of osteomyelitis or sepsis. 5 Therefore, antibiotic therapy should be implemented immediately after identifying the infection in the wound bed to avoid severe complications, such as amputation.
The standard treatment for diabetic foot ulcers (DFU) generally includes cleaning and removal of the necrotic tissue, improving blood circulation, maintenance of a moist environment, and infection control. 6 However, the classic topical therapies for DFU are costly and include low efficacy in the presence of multidrug-resistant bacteria. 4,7 Additionally, topical therapies are cytotoxic and delay healing. 8 Therefore, for DFU, the standard treatment alone is not sufficient for adequate healing and prevention of infections. This fact highlights the relevance of implementing new adjuvant therapies in the treatment of complex ulcers, such as DFU. 3,9 Several studies have suggested photodynamic therapy as a viable option for treating infections in the treatment and healing of DFU. [9][10][11] Photodynamic therapy (PDT) involves the topical application of photosensitizers followed by illumination with Light Amplification by Stimulated Emission of Radiation (LASERs) or Light Emitter Diode (LED) light, which along with tissue oxygen induces the formation of reactive oxygen species and a high local cytotoxic effect, thus The study is relevant in combining the effects and protocols of DFU as an adjuvant therapy in infection reduction, optimizing DFU healing, and offering scientific evidence to reduce bacterial resistance and amputations.

OBJECTIVE
This study aimed to provide a systematic review and meta-analysis of the effectiveness of PDT in the treatment of infected DFU.

Protocol and registry
This systematic review was performed according to the guidelines of the Joanna Briggs Institute (JBI) and the Preferred Reporting Items for Systematic reviews and Metaanalyses (PRISMA). 16,17 It was registered in PROSPERO (CRD42020214187) https://www.crd.york.ac.uk/prospero/ display_record.php?RecordID=214187.

Focal issue
The research question "What is the effectiveness of PDT in the reduction of infection and healing process of infected foot ulcers in patients with DM?" was formulated using the acronym population, intervention, comparison, results, and studies (PICOS).

Study selection
Clinical trials without limitations on the time of publication or language were included if their data were completely available. The following studies were excluded: incomplete studies in annals of events, studies in animal or in vitro models, and studies with ulcers secondary to injuries of other etiologies.

Research strategy and search for scientific evidence
The search was performed between August and December 2020 and reviewed in June 2022. The databases of PubMed, CINAHL, Web of Science, EMBASE, Cochrane Library, Scopus, and LILACS were searched using descriptors, entry terms, and keywords in association with the Boolean operators "AND" and "OR" ( Table 1).

Screening and selection of studies
The screening and selection of studies were performed independently by two reviewers using Rayyan software (Qatar Foundation, Qatar). 18 The complete texts of the selected publications were analyzed by the two reviewers. They evaluated the methodological rigor 19 and capacity to answer the research question. Disagreements were resolved by a third reviewer.

Data extraction
An instrument for data extraction was developed by the authors for the following factors: identification, methodological attributes, PDT protocol, results, limitations, and article recommendations.

Evaluation of the risk of bias, methodological quality, and evidence quality
The risk of bias was graded as low risk of bias, high risk of bias, or uncertain risk of bias using the Cochrane Review Manager v5.4 (Cochrane; London, United Kingdom). 20 The methodological quality was evaluated using a checklist for randomized controlled trials. 19 The evidence quality was evaluated as high, moderate, low, or very low using GRADEpro GDT https://www.gradepro. org/ (Evidence Prime, Kraków, Poland).

Data overview
The extracted data were organized in tables. Review Manager as used for the meta-analyses using a randomized effect model and different averages. Heterogeneity was evaluated statistically using the I 2 test. The meta-analysis was conducted using forest plots.

Description of the included studies
Four of the 76 studies identified were included in the analysis.
Other studies only included ulcers of other etiologies or deviated from the eligibility criteria of this meta-analysis (Flow chart 1). Two evaluated studies did not perform real randomization or hidden allocation. In three cases, blinding was not clear ( Table 2).
In the risk evaluation of bias, the distribution was mainly classified as low-risk (Graphic 1).

Participants
The participants were between 18 and 35 years of age with a confirmed diagnosis of DM and at least one foot ulcer.

Treatment groups
In all studies, PDT was only used in the experimental groups, whereas the control groups were treated with collagenase and chloramphenicol; 21 systemic antibiotics and simple dry bandages; 22 oral antibiotics and gauze embedded in vaseline; 23 or an absorbent cover (Table 3). 24 Review study (n = 07) Study case (n = 05) Studies in animals (n = 02) Abstract from a convention (n = 01) In vitro (n = 01) Injury of other etiology (n = 01) Intervention: primary cover with collagenase 0.6 U/g + chloramphenicol 0.01 g/g.
-Nominal analysis of the ulcers -Healing index of the ulcer -There was an improvement in tissue repair in the patients treated with PDT, especially in the macroscopic aspects of neovascularization, epithelialization, and reduction of the wound's affected area.
-A significant difference in the nominal size of the wounds pre-and post-treatment with PDT was observed along with the wound's affected area (P = 0.036). Intervention: cover with absorption action.

A2
-Microbiological analysis -Nominal analysis of the ulcers -The treatment was well-tolerated without reports of pain.
-There was a significant statistical reduction (P < 0.001) in the bacterial load immediately after PDT; in contrast, there was no significant reduction in the placebo group.
-There was a better healing process-measured using the wound size-in patients who received PDT in comparison with those in the control group.

Outcomes
Two studies 22,24 reported reduced microbial load as the primary outcome and changes in tissue repair as the secondary outcome. Carrinho et al. 21 evaluated the changes in tissue repair as the primary outcome. Tardivo et al. 22 evaluated foot amputation as the primary outcome and changes in tissue repair as the secondary outcome. To measure the effects of PDT on the microbial load, microbiological analyses of ulcer swabs were performed. 23,24 Healing was evaluated using photographs, 22 assessments of the area affected, 21,23 and perfusion, extent, depth, infection and sensation (PEDIS ) score. 23 Radiological assessments and Wagner's classification analysis were used to identify the need for amputation. 22

Main results of PDT in the treatment of foot ulcers
PDT resulted in significant improvements in microbial load and tissue repair compared to the interventions in the control groups. The clinical evolution of the ulcer also demonstrated a significant improvement (P = 0.036) with the use of PDT. 21 PDT also promoted improvements in infection control (P < 0.01). 24 PDT was well-tolerated when compared with the interventions in the control groups. 23 The amputation rate was 35 times lower in the group that received PDT in comparison with the groups that received other treatments (P = 0.002). 22 The most common photosensitizer was methylene blue (0.01% to 1%). The wavelength ranged from 560 nm to 689 nm with doses of 6-30 J/cm 2 .
The number of PDT sessions varied from one to 23. The longest follow-up post-PDT was 90 days ( Table 4).

Quality of evidence
The evidence regarding the outcomes concerning the reduction in the microbial load, improvements in tissue repair, and reduction in amputations was of "moderate quality, " and the outcomes were considered clinically critical (essentials) for the patients.
Therefore, there is moderate confidence in the estimated effect but more clinical trials can improve the confidence ( Table 5).

Effectiveness of PDT in the treatment of foot ulcers with infections
Numerous variabilities were noted in terms of the control groups and the methods of analysis of the evaluated outcomes between the studies. The studies used different parameters in their evaluations, which resulted in high heterogeneity (I 2 = 99%). Therefore, the outcomes of tissue repair were verified in this meta-analysis. However, nested meta-analyses were not performed. The effect of PDT on tissue repair was significant, thus suggesting the benefits of using PDT protocols in DFU.
There were significant differences between the treatments (PDT protocol and standard therapy), and the intervention favored the experimental group (P = 0.04) (Graphic 2).

DISCUSSION
There is a consensus regarding the superiority of PDT treatment for DFU over other therapies in control groups. This finding may be related to PDT's capacity to induce cell death in pathogens, decrease inflammation, and stimulate the proliferation of fibroblasts, collagen, and elastin. 25,26 Owing to its mechanism of action, low invasiveness, and absence of significant collateral effects, PDT offers an alternative treatment for DFU. 27 In the studies evaluated, patients treated with PDT demonstrated a significant reduction in the microbial load. 23,24 Other studies have corroborated this result. 12,28,29 An in vitro study demonstrated that PDT exerted bactericidal effects on resistant bacteria and biofilms through oxidative stress. 10  Several studies have confirmed that PDT is a promising adjuvant approach in the deactivation of resistant bacteria and bacterial biofilms. 10,25,[34][35][36] In two studies, bacterial colonies were decreased shortly after the first PDT session. 23,24 This finding is a relevant benefit since a decrease in the colonies that form the biofilm around the ulcer provides a favorable environment for the formation of healthy granular tissue. 37 Consequently, this deactivation contributes to tissue repair. 12 A better healing process of ulcers was noted with PDT. [21][22][23][24] These findings demonstrate that PDT has several advantages in wound healing, especially in DFU. 1,11 PDT is an adjuvant therapy that can substantially improve the healing process in DFU because it facilitates tissue repair through an immediate reduction in bacterial colonies.
In this study, we identified that through its antimicrobial effects and contribution to the healing process of infected ulcers, No adverse events were associated with PDT. A recent study inferred that with the correct choice of PDT parameters, this approach is safe and reliable. 34 For the three outcomes analyzed, the quality of evidence was considered moderate for an essential clinical outcome. In the meta-analysis, the intervention favored the experimental group. One study corroborated that PDT may be a promising procedure in the management of infected ulcers Graphic 2. Meta-analysis regarding the outcome of tissue repair.
with a higher probability of healing, lower risk of amputation, and an important clinical outcome. 9 However, it is pertinent to discuss the importance of health education with the patients during therapy, especially regarding glycemic control, foot care, use of appropriate shoes, and a healthy lifestyle to improve the success of PDT. 13 The current study contributes to improving the awareness and injured tissues as well as selecting the appropriate LASER parameters and concentration of the photosensitizer to avoid thermal discomfort in the irradiated tissues or phototoxicity.

CONCLUSION
PDT is significantly more effective in treating infected DFU than standard care. A significant reduction in the infection rate was noted soon after the first session of PDT along with an improvement in healing. The three outcomes analyzed were supported by a moderate quality of evidence and essential clinical outcomes.
In the meta-analysis, the intervention significantly favored the groups treated with PDT.